Forwarding packets to a directed acyclic graph destination using link selection based on received link metrics

ABSTRACT

Each network node having at least one destination-oriented link toward a directed acyclic graph (DAG) destination can receive a corresponding set of path performance metrics via the destination-oriented link. The set of path performance metrics, initiated by the DAG destination outputting initial link metrics on each of its source-connecting links, identifies aggregate link metrics for a corresponding path to the DAG destination via the corresponding destination-oriented link. The network node outputs a corresponding updated set of path performance metrics on each of its source-connecting links based on the received set of path performance metrics and the corresponding link metric for the corresponding source-connecting link. Hence, each network node in the DAG can assess the performance of each connected path to the DAG destination, and forward a data packet via a selected destination-oriented link based on the corresponding path performance metrics and forwarding policies for the forwarded data packet.

This application is a continuation of commonly-assigned, copendingapplication Ser. No. 11/255,966, filed Oct. 24, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to creation of a network topologyaccording to a directed acyclic graph for establishment of an ad hocmobile network by mobile routers, and distribution of network traffic toa destination of the directed acyclic graph based on selecting fromamong multiple available paths in the directed acyclic graph.

2. Description of the Related Art

Proposals have been made by Internet Engineering Task Force (IETF)groups for improved mobility support of Internet Protocol (IP) basedmobile devices (e.g., laptops, IP phones, personal digital assistants,etc.) in an effort to provide continuous Internet Protocol (IP) basedconnectivity. The IETF has a Mobile IP Working Group that has developedrouting support to permit IP nodes (hosts and routers) using either IPv4or IPv6 to seamlessly “roam” among IP subnetworks. In addition, theMobile Networks (MONET) group (renamed as the Network Mobility (NEMO)group) has published different Internet Drafts, including an InternetDraft by Thierry Ernst, entitled “Network Mobility Support Terminology”,February 2002. An objective of NEMO is providing mobile nodes withprotocols for establishing connectivity with a wide area network, suchas the Internet. Thus, mobile routers have been used to establish amobile network topology in order to route packets between the mobilenetwork and the Internet via a gateway at an edge of the mobile network.However, such a mobile network topology typically requires an aggregatereachability to IP nodes, where all nodes sharing a common network link(such as a link of a top level mobile router connecting to an attachmentrouter on the Internet) share the same routing prefix. Such aggregationcreates a hierarchy of network prefixes that enables scalability.However, such a hierarchy is not possible in ad hoc networks.

The IETF has a Mobile Ad-hoc Networks (MANET) Working Group that isworking to develop standardized MANET routing specification(s) foradoption by the IETF. According to the MANET Working Group, the “mobilead hoc network” (MANET) is an autonomous system of mobile routers (andassociated hosts) connected by wireless links—the union of which form anarbitrary graph. The routers are free to move randomly and organizethemselves arbitrarily; thus, the network's wireless topology may changerapidly and unpredictably. Such a network may operate in a standalonefashion, or may be connected to the larger Internet.

The MANET system is particularly suited to low-power radio networks thatmay exhibit an unstable topology, where wireless propagationcharacteristics and signal quality between a wireless transmissionsource and a receiver can be difficult to model and quantify. In aMANET, the device address is tied to the device, not a topologicallocation, as there is no fixed network infrastructure. When theaddressed device moves, therefore, the motion changes the routinginfrastructure. Hence, as described in an Internet Draft by Baker,entitled “An Outsider's View of MANET” (Mar. 17, 2002), the fundamentalbehavior of a MANET is that a routing node carries with it an address oraddress prefix, and when it moves, it moves the actual address; whenthis happens, routing must be recalculated in accordance with the newtopology. For example, each mobile router retains its address prefix;hence, neighboring mobile routers in a MANET may have distinct addressprefixes.

FIG. 1 is a diagram illustrating a conventional layer 2 mesh network 10having multiple mobile routers (N0, N1, N2, N3, N4) interconnected bylinks (A, B, C, D, E, F, G) having respective metrics (i.e., costs). Thepresence of layer 2 links (A, B, C, D, E, F, G), however, does notprovide a routing topology that enables any given mobile router to reacha destination mobile router. Hence, a routing protocol such as OpenShortest Path First (OSPF) (as specified by the IETF Request forComments (RFC) 2178) has been needed in order for each mobile router(e.g., N0) to determine a path to a given destination (e.g., N11).

Communications between mobile routers of an ad hoc network can beoptimized based on the mobile routes organizing into a tree-basedtopology. For example, U.S. Patent Publication No. US 2004/0032852,published Feb. 19, 2004, entitled “Arrangement for Router AttachmentsBetween Roaming Mobile Routers in a Mobile Network”, the disclosure ofwhich is incorporated in its entirety herein by reference, describes atechnique for each mobile router of an ad hoc mobile network toindependently select whether to attach to a candidate attachment router,based on tree information options advertised by the candidate attachmentrouter and selection criteria employed by the mobile router. Theindependent selection by each router of whether to attach to anotherrouter enables the routers to dynamically establish a tree-based networktopology model, where each router may continually determine whether analternate attachment point within the tree is preferred.

Link reversal routing has been suggested as a technique for providingmultiple communications links between nodes in an ad hoc mobile network,where link reversal routing algorithms build a directed acyclic graph(DAG) for each possible destination: a directed graph is acyclic if itcontains no cycle or loop, and the DAG maps to a given destination basedon the destination having only incoming links: all other nodes that haveincoming links also must have outgoing links. An example of a routingalgorithm that builds a DAG is the Temporally-Ordered Routing Algorithm(TORA).

Commonly-assigned, copending application Ser. No. 11/167,240, filed Jun.28, 2005, entitled “Directed Acyclic Graph Discovery and Network PrefixInformation Distribution Relative to a Clusterhead in an Ad Hoc MobileNetwork”, published Dec. 28, 2006 as U.S. Patent Publication No.2006/0291404 (the disclosure of which is incorporated in its entiretyherein by reference), describes one technique for creating a directedacyclic graph, where each mobile router in an ad hoc mobile network isconfigured for concurrently attaching to multiple parents advertisingrespective parent depths relative to a clusterhead of the ad hoc mobilenetwork. The mobile router selects an advertised depth relative to theclusterhead based on adding a prescribed increment to a maximum one ofthe parent depths, enabling the mobile routers to form a directedacyclic graph relative to the clusterhead. Each mobile router sends toeach of its parents a neighbor advertisement message specifyinginformation that enables the parents to reach at least one reachableprefix relative to stored router entries.

Another example of a directed acyclic graph creation in an ad hocnetwork is described in commonly-assigned, copending application Ser.No. 11/251,765, filed Oct. 18, 2005, entitled “Directed Acyclic GraphComputation by Orienting Shortest Path Links and Alternate Path LinksObtained from Shortest Path Computation”, published Apr. 19, 2007 asU.S. Patent Publication No. 2007/0086358, the disclosure of which isincorporated in its entirety by reference. The network node performs amodified shortest path first calculation by identifying next-hop nodesadjacent to the network node, and orienting the link of each next-hopnode toward itself (i.e., the origin). The network node also identifiessecondary adjacent nodes, adjacent to each of the next hop nodes, andextends paths from next-hop nodes to the associated secondary adjacentnodes while orienting each of the links of the path between adjacentnodes and next-hop nodes toward the next hop nodes. The paths of thenodes form a directed acyclic graph from any other network node towardthe origin, enabling distribution of the directed acyclic graph to theother network nodes for optimized reachability to the network node.

Although the foregoing description demonstrates that directed acyclicgraphs can be readily created within an ad hoc network, a typicalimplementation would result in full utilization of the shortest pathtoward a DAG destination, with no utilization of any other path in theDAG until the shortest path was no longer available. Efforts to improvethe performance of link state routing computations, also referred toShortest Path First (SPF) based computations, based on using dynamicrouting metrics instead of static metrics previously resulted in networkinstability. For example, in OSPF a router floods the network with linkstate advertisements (LSAs) advertising the assigned costs of therespective links utilized by the router, enabling other routers tocalculate shortest routes to destinations. Use of dynamic routingmetrics (e.g., early attempts at using dynamic routing metrics (e.g., inARPANET)) were unsuccessful because the dynamic routing metrics tendedto introduce instabilities due to oscillation in the link delay values:routers receiving an advertisement of a dynamic routing metric (e.g., alow link delay value in a delay-based routing protocol) wouldimmediately reconfigure their routes to use the advertised low delaylink, creating substantially higher traffic on the advertised link;routers would then reroute their paths around the advertised link thathad become a high delay link, causing the router to advertise theadvertised link again as a low delay link. Such oscillation in thedynamic routing metrics caused routing instability.

Load balancing technology has been implemented in conventional InternetProtocol based networks that have an established addressing hierarchy.For example Enhanced Interior Gateway Routing Protocol (EIGRP)(described in U.S. Pat. No. 5,519,704 and incorporated in its entiretyherein by reference) permits unequal-cost load balancing. However, EIGRPis a distance vector-based routing protocol and therefore incompatiblewith OSPF-based routing protocols, and therefore cannot be used innetworks that rely on directed acylic graphs.

Other proposals such as Reservation Protocol with Traffic Engineering(RSVP-TE) according to RFC 3209 require best paths to be regularlyrecomputed using Constrained Shortest Path First (CSPF) (RFC 4105),which causes a loss of routing capabilities until the new best pathshave been established. In addition, such proposals require source-routecapabilities, which introduces the necessity of maintaining path statesthroughout a path in the network.

SUMMARY OF THE INVENTION

There is a need for an arrangement that optimizes utilization of allavailable paths in a directed acyclic graph (DAG) toward a DAGdestination, without the necessity of route recalculation that wouldrequire recalculation of the DAG.

There also is a need for an arrangement that enables each network nodein a path toward a DAG destination to determine how network trafficshould be distributed among multiple next-hop links toward a DAGdestination.

There also is a need for an arrangement that optimizes utilization ofall available paths in a directed acyclic graph (DAG) toward a DAGdestination, without the necessity of maintaining state information fora given path.

These and other needs are attained by the present invention, where eachnetwork node having at least one destination-oriented link toward adirected acyclic graph (DAG) destination is configured for receiving acorresponding set of path performance metrics via the at least onedestination-oriented link. The set of path performance metrics,initiated by the DAG destination outputting initial link metrics on eachof its source-connecting links, identifies aggregate link metrics for acorresponding path to the DAG destination via the correspondingdestination-oriented link. The network node outputs a correspondingupdated set of path performance metrics on each of its source-connectinglinks based on the received set of path performance metrics and thecorresponding link metric for the corresponding source-connecting link.Hence, each network node in the DAG is able to assess the performance ofeach connected path toward the DAG destination, and forward a datapacket via a selected destination-oriented link based on thecorresponding path performance metrics and forwarding policies for theforwarded data packet.

One aspect of the present invention provides a method in a network node.The method includes receiving, via a first destination-oriented linkthat is directed toward a directed acyclic graph (DAG) destination, afirst set of path performance metrics that identifies aggregate linkmetrics for a corresponding path to the DAG destination via the firstdestination-oriented link, the path performance metrics based on atleast initial link metrics having been output by the DAG destinationonto a corresponding source-connecting link, the initial link metricsdescribing performance of the corresponding source-connecting link. Themethod also includes selectively determining second link metrics foreach second source-connecting link connecting the network node to acorresponding connected network node. The method also includesselectively outputting, onto each second source-connecting link, acorresponding updated set of path performance metrics based on the setof path performance metrics and the corresponding second link metrics,the updated set of path performance metrics identifying the aggregatelink metrics for the corresponding path to the DAG destination via thecorresponding second source-connecting link and the firstdestination-oriented link.

The distribution of path performance metrics, identifying the aggregatelink metrics for the links establishing a path to the DAG destination,enables each network node to determine the relative aggregate linkmetrics for each available path toward the DAG destination. Hence, eachnetwork node can dynamically select a destination-oriented link forforwarding a data packet to the DAG destination, based on the relativeaggregate link metrics.

Consequently, a network node can quickly adapt to changes in networkactivity, for example a deteriorating condition in an available path dueto a corresponding deteriorating condition in a remotedestination-oriented link of another network node in the path, whilepreserving utilization of the existing directed acyclic graph. Further,link layer traffic policies (including bandwidth reservation policies)can be implemented throughout the network based on distribution of theaggregate link metrics based on establishing a forwarding procedureoverlying the directed acyclic graph. Hence, network traffic can bererouted as needed along different paths toward the DAG destinationwithout any modification or recalculation of the directed acyclic graph.

Additional advantages and novel features of the invention will be setforth in part in the description which follows and in part will becomeapparent to those skilled in the art upon examination of the followingor may be learned by practice of the invention. The advantages of thepresent invention may be realized and attained by means ofinstrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is made to the attached drawings, wherein elements having thesame reference numeral designations represent like elements throughoutand wherein:

FIG. 1 is a diagram illustrating a conventional (prior art) layer 2 meshnetwork.

FIG. 2 is a diagram illustrating the network of FIG. 1 havingestablished a directed acyclic graph (DAG) for reaching a DAGdestination along selected paths based on distribution of link metrics,according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating one of the network nodes of FIG. 2,according to an embodiment of the present invention.

FIGS. 4A and 4B are diagrams illustrating alternative implementations ofthe path performance metrics as a collected set of link metrics for eachhop in a path, and a set of accumulated link metrics for each path,respectively.

FIG. 5 is a diagram illustrating the method in the network of FIG. 2,and in each of the mobile nodes of FIG. 2, of distributing pathperformance metrics to enable selection of destination-oriented linksalong a selected path, according to an embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 2 is a diagram illustrating the layer 2 mesh network of FIG. 1having established a directed acyclic graph (DAG) 12 for reaching a DAGdestination 14 along selected paths, based on distribution of linkmetrics, according to an embodiment of the present invention. Inparticular, the DAG 12 enables any source node 16 to send data to theDAG destination 14 via at least one path. The directed acyclic graph 12,generated by the DAG destination N0 14, also referred to as the“origin”, is distributed to each of the other network nodes 16 (N1, N2,N3, and N4), enabling each of the other nodes 16 (N1, N2, N3, and N4) toestablish at least one path to the DAG destination N0 based onforwarding data via successive destination-oriented links A, B, C, D, E,F, or G.

The term “destination-oriented link” refers to any link that transmitsdata from a network node to either the DAG destination 14, or a next-hopnode 16 having a corresponding destination-oriented link fortransmitting data packets toward the DAG destination 14 via a loop-freepath. For example, the network node N2 has a destination-oriented link Cfor transmitting data packets to the DAG destination 14, and a seconddestination-oriented link D for transmitting data packets to the DAGdestination 14 via the next-hop network node N1; in contrast, thenetwork node N2 has source-connecting links E and F that enable therespective source nodes N3 and N4 to reach the DAG destination 14 viaone of the destination-oriented links C or D. Also note that thesource-connecting links E and F cannot be used by the network node N2for reaching the DAG destination 14 (N0), as the structure of the DAG 12requires that data traffic destined for the DAG destination 14 travel inthe indicated direction (i.e., link E is used to transmit data only fromnetwork node N3 to N2 and link F is used to transmit data only from thenetwork node N4 to N2). Hence, the single destination-oriented link B ofthe network node N1 is the only available link for the network node N1to transmit data packets to the DAG destination 14, as the link D is asource-connecting link for the network node N1.

As described above, the establishment of destination-oriented links andsource-connecting links between the network nodes establishing the DAG12 guarantees that any data packets from any of the source nodes 16 willreach the DAG destination 14, assuming the packet is not dropped. Forexample, the network node N4 is able to reach the DAG destination 14 viafive distinct paths: the first path is formed by thedestination-oriented links F-C; the second path is formed by thedestination-oriented links F-D-B; the third path is formed by thedestination-oriented links G-E-C; the fourth path is formed by thedestination-oriented links G-E-D-B; and the fifth path is formed by thedestination-oriented links G-A. Hence, the DAG 12 guarantees that anypacket output by the network node N4, or any other node N3, N2, or N1will invariably reach the DAG destination 14, unless for some reason thepacket is dropped.

As described previously, there is a need for an arrangement thatoptimizes utilization of all available paths in the DAG 12 toward theDAG destination 14, without the necessity of route recalculation thatwould require recalculation of the DAG 12. For example, it would behighly desirable for the network node N4 to be able to select one of theavailable destination-oriented links F or G on a per-packet basis, inorder to implement traffic policies such as load-balancing, bandwidthreservation according to prescribed protocols such as resourcereservation protocol, etc.

According to the disclosed embodiment, the directed acyclic graph 12 isgenerated by the origin 14 based on topological metrics that are used toestablish a network topology within a network. In particular,topological metrics refer to network parameters that are static, or thatchange only infrequently, for example access router identifier, serviceprovider identifier, link speed, link bandwidth, and other parametersthat may be manually configured by network administrators. Suchtopological metrics typically have a correlation between their valuesand a corresponding cost of utilizing the associated link that connectsnetwork nodes.

Consequently, topological metrics are used by the origin 14 in order tocreate the DAG 12, which can then be distributed to the other nodes 16in order to enable the other nodes 16 to reach the origin 14 viamultiple available paths. As apparent from the foregoing, each networknode N0, N1, N2, N3, N4 will create its own directed acyclic graphtowards itself, and distribute the corresponding directed acyclic graphto the other nodes. Hence, each of the nodes have, for each other nodein the network 10, a corresponding DAG 12 for reaching the correspondingDAG destination 14.

Following establishment of the DAG 12, each of the network nodes alsoestablishes a forwarding protocol that enables network traffic to theDAG destination 14 to be balanced across the availabledestination-oriented links, without modifying the structure of the DAG12. Further, the periodic distribution (i.e., cascading) of pathperformance metrics P1, P2, P3, P4, P5, P6 and P7 initiated by the DAGdestination 14 enables each of the other network nodes 16 to adapt theirrespective forwarding protocols based on the detected path performancemetrics P1, P2, P3, P4, P5, P6 and P7, without any modification to theunderlying DAG 12.

As described in further detail below, the DAG destination 14 initiallyoutputs, on each of its source-connecting links A, B, and C, acorresponding set of initial link metrics P1, P2, and P3 that describedynamic metrics (i.e., metrics that vary based on network traffic,resource reservation requests, etc.) for the correspondingsource-connecting links A, B, and C. The next-hop nodes N3, N1, and N2,in response to receiving the initial link metrics P1, P2, and P3 viatheir respective destination-oriented links A, B, and C, store theinitial link metrics internally; each of the next-hop nodes N3, N1, andN2 also determine the associated link metrics for each of theirsource-connecting links (e.g., G for N3, D for N1, and links E and F forN2) and output a corresponding updated set of path performance metrics(P7 by N3 onto G; P4 by N1 onto D; and P5 onto E and P6 onto F by N2)that identify the aggregate link metrics for the corresponding path tothe DAG destination 14 via the corresponding source-connecting link anddestination-oriented link. Each link metric includes a DAG originidentifier that identifies the DAG destination 14, and a sequence numberthat uniquely identifies the link metric. Identification of the DAGdestination 14 (N0) by the DAG origin identifier enables a network node16 to identify that a received link metric is associated with a linkmetric propagation that has been initiated by the DAG destination 14(N0), and therefore is relevant to the DAG 12 oriented toward the DAGdestination 14 (N0). In addition, the sequence number enables any nodeto determine whether the received link metric associated with the DAG 12oriented toward the DAG destination 14 (N0) is the most recent metricrelative to prior received metrics.

Hence, each network node 16 can obtain precise metrics with respect toavailable paths for reaching a specific destination, namely the DAGdestination 14. The precise metrics for the available paths to thedestination enables each network node to assess traffic distributionthroughout the DAG 12 for reaching the DAG destination 14, and performdestination-oriented link selection in order to evenly distributenetwork traffic throughout the DAG 12.

Consequently, network traffic can be balanced to the extent that eachand every path can reach saturation before the need for dropping anypacket; further, such dynamic forwarding protocols enable the networkthroughput to be improved, since at least some of traffic can bedynamically rerouted via a less congested loop less path. Hence, theestablishment of a forwarding protocol overlying the DAG 12, having beencreated according to a prescribed routing protocol, enablesimplementation of a graph-level out-of-band flow control resource thatinfluences forwarding decisions in order to reroute traffic overflow,and which tends to restore initial settings upon normal networkconditions.

FIG. 3 is a diagram illustrating one of the network nodes 14 or 16 ofFIG. 2, according to an embodiment of the present invention. For ease ofillustration, FIG. 3 illustrates the network node N2 having thedestination-oriented links 18 (C and D) and the source-connecting links20 (E and F). The network node 16 of FIG. 3 includes a network interface22, a routing resource 24 configured for generating its own DAG 12(i.e., where the node N2 establishes itself as the DAG destination)based on topological metrics, and a DAG table 26 configured for storingthe DAG 12 for each of the other network nodes as respective DAGdestinations (e.g., the DAG 12 of FIG. 2). The node 16 also includes anexecutable link resource 28, a link status table 30, and a means 32 aand/or 32 b for storing the path performance metrics for each of thepaths reachable by a corresponding destination-oriented link 18. Asdescribed below, the means for storing the path performance metrics foreach path toward the DAG destination 14 may be implemented either as apath metrics table 32 a or a link state table 32 b.

The network interface 22 is configured for receiving, via thedestination-oriented links 18, path performance metrics that identifyaggregate link metrics for each path to the DAG destination 14. Forexample, FIG. 2 illustrates that the network interface 22 receives, viathe destination-oriented link C, a first set of path performance metricsP3 that identifies the aggregate link metrics for the corresponding path(via link C) to the DAG destination 14 via the destination-oriented linkC having supplied the path performance metrics; in this case, the pathperformance metrics P3 simply specify the initial link metrics for thelink C having been output by the DAG destination 14 P3. FIG. 2 alsoillustrates that the network interface 22 receives, via the seconddestination-oriented link D, a second set of path performance metrics P4that identifies the aggregate link metrics for the corresponding path(via links D-B) to the DAG destination 14 via the seconddestination-oriented link D having supplied the path performance metricsP4.

Each of the path performance metrics (e.g., P3, P4) received by thenetwork interface 22 identifies aggregate link metrics for acorresponding path (e.g., via link C, or via links D-B) to the DAGdestination 14 via the corresponding destination-oriented link. The pathperformance metrics (e.g., P3 or P4) may be implemented either as acollection of individual link metrics for each hop in the correspondingpath between the DAG destination 14 and the network node having receivedthe path performance metrics, or a single message that specifies theaggregate link metrics for the links along the corresponding path.

FIGS. 4A and 4B are diagrams illustrating alternative exemplaryimplementations of the path performance metrics as distributedthroughout the DAG 12. FIG. 4A illustrates a link state type of pathperformance metrics, where each path performance metric 40 is composedof a corresponding collection 42 of individual link metrics 44: eachindividual link metric 44 specifies the link metrics for a specific link(e.g., link C), such that a network node 16 receives the metrics foreach link for each hop to the DAG destination 14. In particular, eachindividual link metric 44 (e.g., PC) specifies a link identifierspecifying the specific link being measured (e.g., C), the DAG originidentifier (identifying that the link metric 44 is relevant to the DAG12 oriented toward the DAG destination 14 (N0), and the sequence number.The network interface 22 may receive the collection 42 of individuallink metrics 44 as a plurality of individual messages having the sameDAG origin identifier and sequence number and respective linkidentifiers, where the individual link metrics 44 for a given collection42 may need to be received within a prescribed timer interval.

As described below, each network node 16, in response to receiving acollection 42 of individual link metrics 44 that form a path performancemetric 40, updates the collection of path performance metrics byoutputting onto each source-connecting link the received collection 42of individual link metrics 44, and also outputting its own correspondinglink metrics for each source-connecting link. For example, in responseto receiving via link C the path performance metrics P3 (consisting ofthe individual link metric PC 44 for link C) and the individual linkmetrics PB and PD 44 that form the path performance metrics P4, the linkresource 28 will store the received metrics in the table 32 b anddetermine the link metrics (e.g., PE, PF) for each source-connectinglink (e.g., link E, link F) as stored as entries 31 a, 31 b in the linkstatus table 30 of FIG. 3; the link resource 28 outputs onto thesource-connecting link E the individual link metrics PB, PC, PD, and PE(which constitute the path performance metric P5 40), each specifyingthe same DAG origin identifier and the same sequence number as receivedvia links C and D. The link resource 28 also outputs onto thesource-connecting link F the individual link metrics PB, PC, PD, and PF(which constitute the path performance metric P6 40), each specifyingthe same DAG origin identifier and the same sequence number as receivedvia links C and D.

Although the above description assumes that the path performance metric40 is composed of receiving a collection of individual messages eachspecifying a corresponding link metric 44, where membership in thecollection is based at least on DAG origin identifier and sequencenumber (and possibly also by receipt within a timer window), analternative implementation for the path performance metric 40 is thatthe entire collection 42 is sent as a single message containing multiplelink metrics 44.

Hence, the link resource 28 stores the received link metrics 44 for eachof the path performance metrics 40 in the link state table 32 b. Inparticular, the link resource 28 stores each of the link metrics 44, foreach hop in the path between the DAG destination 14 and the networknode, in the link state table 32 b in the form of a table entry 36. Asillustrated in FIG. 4A the set of path performance metrics P4 is acollection of the link metrics PB and PD generated by the nodes N0 andN1, respectively. Hence, the link resource 28 stores the link metrics PBand PD as entries 36 a and 36 c, respectively.

Each entry 36 includes the associated link metrics for the correspondinglink, including exemplary parameters such as bandwidth or trafficutilization 37 a, signal to noise ratio 37 b, gain 37 c, link speed 37d, and bandwidth reservation level 37 e. Hence, each set of link metrics44 specifies the parameters 37 a-37 e, enabling the link resource 28 todetermine the path performance metrics for paths toward the DAGdestination 14 based on parsing the link state table for each of thenext-hop links toward the DAG destination 14.

FIG. 4B illustrates an alternative form of path performance metrics,namely a distance vector type of path performance metric, where eachpath performance metric 46 specifies at least one set of accumulatedlink metrics 48 for a corresponding path, where each accumulated linkmetric 48 is composed of the link metrics 44 for at least the initiallink metrics for a source-connecting link from the DAG destination 14.For example, the path performance metric P4 specifies the accumulatedlink metrics 48 describing the corresponding path (D-B) to the DAGdestination 14, where the accumulated link metrics 48 are expressed as“PB+PD”: note that the plus sign “+” does not represent addition,especially since addition is not performed; rather each of theassociated link metrics 37 are accumulated (i.e., cumulatively compared)as appropriate, for example identifying a minimum value for “weakestlink” analysis (e.g., worst traffic utilization 39 a that is mostcongested, lowest signal to noise ratio 39 b, lowest gain 339 c, lowestlink speed 39 d), identifying a maximum value for maximum reservedbandwidth 39 e, etc.

Hence, FIG. 4B illustrates that the path performance metrics P1, P2, P3,and P4 identify the aggregate link metrics 48 for a single path, whereasthe path performance metrics P5 and P6 each identify the aggregate linkmetrics 48 for two distinct paths to the DAG destination 14, and thepath performance metric P7 identifies the aggregate link metrics 48 forthree distinct paths to the DAG destination 14.

Referring to FIG. 3, the link resource 28, in response to receiving thepath performance metric P3 46, stores in the path metrics table 32 a aforwarding table entry 38 a specifying that the DAG destination 14 isreachable via the destination-oriented link C according to theaccumulated link metrics 39 a-39 e: since the path performance metric P346 is output by the DAG destination 14 as the initial link metricdescribing the performance of its corresponding source-connecting linkP3, the entry 38 a of the node N2 specifies simply the initial linkstate metrics for its destination-oriented link C. In contrast, the linkresource 28 responds to receipt of the path performance metric P4 46 bystoring in the path metrics table 32 a a forwarding table entry 38 bthat specifies that the DAG destination 14 is reachable via thedestination-oriented link D according to the accumulated link metrics 39a-39 e. As described previously, the accumulated link metrics may beexpressed as minimum values, maximum values, accumulated values, ormoving averages (e.g., average value per hop), as appropriate.

FIG. 5 is a diagram illustrating the method in the network nodes of theDAG 12 of distributing path performance metrics for selection ofdestination-oriented links along a selected path, according to anembodiment of the present invention. The steps described in FIG. 5 canbe implemented as executable code stored on a computer readable medium(e.g., a hard disk drive, a floppy drive, a random access memory, a readonly memory, an EPROM, a compact disk, etc.).

The method begins in step 60, where the DAG destination 14 calculatesand distributes the DAG topology 12 to the other nodes 16. Additionaldetails related to creation of the DAG 12 are disclosed in theabove-incorporated application Ser. Nos. 11/167,240 and 11/251,765.

The other nodes 16 store the appropriate paths for the DAG 12 in theirDAG table 26 in step 62, providing each node 16 at least one path to theDAG destination 14. Once each node 16 has stored the at least one pathin the DAG table 26, the node 16 can begin forwarding data packets tothe DAG destination 14.

The DAG destination 14 begins monitoring link status of itssource-connecting links A, B, and C, stores the link status results inits corresponding link status table 30, and periodically outputs in step64 the path performance metrics P1, P2, P3 (containing only the initiallink metrics PA, PB, and PC respectively) via the respectivesource-connecting links A, B, and C, resulting in the network nodes N3,N1, and N2 receiving the respective initial link metrics P1, P2, and P3.As described previously, each of the initial link metrics PA, PB, and PCspecify the same DAG origin identifier (N0) and the same sequence numberto identify a new “event” for refreshing the link metrics in the DAG 12.Each of the network nodes N3, N1, and N2 receiving the initial linkmetrics update the path performance metrics for the new “event” anddistribute the updated path performance networks on theirsource-connecting links oriented away from the DAG destination 14.

Hence, the initial link metrics PA, PB, and PC output by the DAGdestination (N0) 14 initiate a “cascade” of path performance metricsthroughout the DAG 12.

The remainder of the steps in FIG. 5 will be described with respect tothe network node N2 of FIG. 3 for simplicity, although it will bereadily apparent that the steps described herein apply to each of thenodes 16.

The network interface 22 of the network node N2 16 receives in step 66the path performance metrics for a given path via a destination-orientedlink: as described previously, the network node N2 receives the pathperformance metrics P3 and P4 via the respective destination-orientedlinks C and D. In the case of the path performance metric P3, the linkresource 28 stores the path performance metrics P3 either as a pathmetrics table entry 38 a or a link state table entry 36 b, depending onimplementation; if both types of path performance metrics are used inthe DAG 12, then since the path performance metric P3 specifies a singlehop link metric, the link resource 28 may store the entries 38 a and 36b as identical entries.

In the case of the path performance metric P4 received via thedestination-oriented link D, the link resource 28 stores the pathperformance metric P4 as a path metric table entry 38 b (assuming themetric P4 specifies the aggregate link metrics as a set 48 ofaccumulated link metrics), or as link state table entries 36 a and 36 d(based on the path performance metrics P4 being expressed as acollection of link metrics 44 specifying the same sequence number). Asapparent from the foregoing, the network interface 22 may receive thepath performance metrics P4 as individual messages, each messagecarrying a corresponding link state metric 44; hence, network interface22 may receive the link state metrics PB and PD via thedestination-oriented link D as separate messages, where the separatemessages specifying the link state metrics PB and PD in combinationconstitute the path performance metric P4.

The link resource 28 determines in step 68 the connecting link metricsspecified in the link status table 30 for each source-connecting link Eand F. As described previously, the link resource 28 continuallymonitors the status of the source-connecting links E and F, and updatesthe link status table entries 31 a and 31 b accordingly. The linkresource 28 aggregates the link metrics of the source-connecting links Eand F with the received aggregate link metrics in step 70, and outputsthe updated set of path performance metrics onto the appropriatesource-connecting link, depending on implementation.

For example, in the case of link state type path performance metrics,the link resource 28 may simply repeat the received link metrics PB, BC,and PD on each of the source-connecting links E and F in step 72, andoutput also in step 72 link metrics PE onto the correspondingsource-connecting link E, and output link metrics PF onto thecorresponding source-connecting link F. Alternately, the link resource28 may collect in step 70 all of the received link metrics, and appendin step 70 the appropriate link metric; hence, the link resource 28could output in step 72 the path performance metrics P5 and P6, asillustrated in FIG. 4A, as a single message specifying each of the linkmetrics for each hop in the path between the DAG destination 14 and thecorresponding source-connecting link.

If the path performance metrics are implemented as accumulated linkmetrics as illustrated in the path metrics table 32 a, the link resource28 accumulates (i.e., cumulatively compares) in step 70 the connectinglink metrics specified in the link status entries 31 a and 31 b with theaccumulated metrics for the destination-oriented links as specified inthe path metrics table entries 38 a and 38 b. The link resource 28outputs the updated set of accumulated link metrics that describe a pathbetween the DAG destination 14 and the corresponding source-connectinglink, as illustrated as the path performance metrics P5 and P6 of FIG.4B.

The link resource 28 repeats the process for each source-connecting linkin step 74, such that each connected network node receives theappropriate updated metrics. As apparent from the foregoing, eachnext-hop node repeats the above-described process in step 76, enablingeach network node 16 to identify the metrics for each path toward theDAG destination 14.

The link resource 28 in each network node therefore can utilize thestored path performance metrics in order to choose whether a given datapacket should be forwarded over a given destination-oriented link instep 78. As apparent from the foregoing, the distribution of pathperformance metrics from the DAG destination 14 throughout the DAG 12enables each of the network nodes 16 to continually assess theperformance of a given path in reaching the DAG destination 14.Consequently, packets can be rerouted or distributed along various pathsdepending on the path performance metrics, and forwarding policies forgiven packets. For example, implementation of bandwidth reservationpolicies (e.g., according to RSVP protocol) enables packets identifiedas belonging to the reserved bandwidth to be forwarded along a pathhaving the reserve bandwidth, whereas other packets that do not belongto the reserve bandwidth may be forwarded along different routes.Further, detected congestion conditions on various links may cause aredistribution of traffic flows, without the necessity of modifying theDAG 12.

According to the disclosed embodiment, network traffic is forwarded viamultiple available paths to a DAG destination, based on partitioning therouting protocol that defines the DAG, from traffic forwarding protocolsthat utilize the DAG to choose forwarding paths based on detected linktraffic conditions.

While the disclosed embodiment has been described in connection withwhat is presently considered to be the most practical and preferredembodiment, it is to be understood that the invention is not limited tothe disclosed embodiments, but, on the contrary, is intended to covervarious modifications and equivalent arrangements included within thespirit and scope of the appended claims.

1. A method in a network node, the method including: receiving, via afirst link of the network node, a first set of path performance metricsthat identifies aggregate metrics for a corresponding path to aprescribed destination via the first link, the path performance metricsbased on at least initial link metrics having been output by theprescribed destination onto a corresponding source-connecting link ofthe prescribed destination, the initial link metrics describingperformance of the corresponding source-connecting link of theprescribed destination; selectively determining second metrics for atleast a second source-connecting link providing reachability by thenetwork node to the prescribed destination for at least one connectednetwork node; and outputting, onto the second source-connecting link, anupdated set of path performance metrics based on the first set of pathperformance metrics and the second metrics, the updated set of pathperformance metrics identifying the aggregate metrics for thecorresponding path to the prescribed destination via the secondsource-connecting link and the first link; wherein the prescribeddestination is identified by the network node as a directed acyclicgraph (DAG) destination and the first link is selected by the networknode as a destination-oriented link that is directed toward the DAGdestination.
 2. The method of claim 1, further comprising: secondreceiving, via a second link of the network node, a second set of pathperformance metrics that identifies the aggregate metrics for acorresponding path to the prescribed destination via the second link;and selecting one of the first or second links, based on a comparisonbetween the first and second set of path performance metrics.
 3. Themethod of claim 2, further comprising second outputting a correspondingsecond updated set of path performance metrics based on the second setof path performance metrics and the second metrics, the second updatedset of path performance metrics identifying the aggregate metrics forthe corresponding path to the prescribed destination via the networknode.
 4. The method of claim 3, wherein: the aggregate metrics for eachof the first and second set of path performance metrics are specified asa corresponding plurality of link metrics for each hop in thecorresponding path between the prescribed destination and the networknode.
 5. The method of claim 1, wherein the initial link metrics includeat least one of bandwidth utilization, signal to noise ratio, signalstrength, selected link speed, or bandwidth reservation level.
 6. Anetwork node comprising: a network interface configured for receiving,via a first link, a first set of path performance metrics thatidentifies aggregate metrics for a corresponding path to a prescribeddestination via the first link, the path performance metrics based on atleast initial link metrics having been output by the prescribeddestination onto a corresponding source-connecting link of theprescribed destination, the initial link metrics describing performanceof the corresponding source-connecting link of the prescribeddestination; and a resource configured for: selectively determiningsecond metrics for at least a second source-connecting link providingreachability by the network node to the prescribed destination for atleast one connected network node, and outputting, onto the secondsource-connecting link having been established by the network interfacewith the connected network node, an updated set of path performancemetrics based on the first set of path performance metrics and thesecond metrics, the updated set of path performance metrics identifyingthe aggregate metrics for the corresponding path to the prescribeddestination via the second source-connecting link and the first link;wherein the prescribed destination is identified by the network node asa directed acyclic graph (DAG) destination and the first link isselected by the network node as a destination-oriented link that isdirected toward the DAG destination.
 7. The network node of claim 6,wherein: the network interface is configured for receiving, via a secondlink of the network node, a second set of path performance metrics thatidentifies the aggregate metrics for a corresponding path to theprescribed destination via the second link; the resource configured forselecting one of the first or second links, based on a comparisonbetween the first and second set of path performance metrics.
 8. Thenetwork node of claim 7, wherein the resource is configured foroutputting a corresponding second updated set of path performancemetrics based on the second set of path performance metrics and thesecond metrics identifying the aggregate metrics for the correspondingpath to the prescribed destination via the network node.
 9. The networknode of claim 8, wherein: the aggregate metrics for each of the firstand second set of path performance metrics are specified as acorresponding plurality of link metrics for each hop in thecorresponding path between the destination and the network node.
 10. Thenetwork node of claim 6, wherein the initial link metrics include atleast one of bandwidth utilization, signal to noise ratio, signalstrength, selected link speed, or bandwidth reservation level.
 11. Anon-transitory computer readable medium having stored thereon sequencesof computer executable instructions for a network node to establishcommunications toward a prescribed destination, the sequences ofcomputer executable instructions including instructions for: receiving,via a first link of the network node, a first set of path performancemetrics that identifies aggregate metrics for a corresponding path tothe prescribed destination via the first link, the path performancemetrics based on at least initial link metrics having been output by theprescribed destination onto a corresponding source-connecting link ofthe prescribed destination, the initial link metrics describingperformance of the corresponding source-connecting link of theprescribed destination; selectively determining second metrics for atleast a second source-connecting link providing reachability by thenetwork node to the prescribed destination for at least one connectednetwork node; and outputting, onto the second source-connecting link, anupdated set of path performance metrics based on the first set of pathperformance metrics and the second metrics, the updated set of pathperformance metrics identifying the aggregate metrics for thecorresponding path to the prescribed destination via the secondsource-connecting link and the first link; wherein the prescribeddestination is identified by the network node as a directed acyclicgraph (DAG) destination and the first link is selected by the networknode as a destination-oriented link that is directed toward the DAGdestination.
 12. The medium of claim 11, further comprising instructionsfor: second receiving, via a second link of the network node, a secondset of path performance metrics that identifies the aggregate metricsfor a corresponding path to the destination via the second link; andselecting one of the first or second links, based on a comparisonbetween the first and second set of path performance metrics.
 13. Themedium of claim 12, further comprising instructions for secondoutputting a corresponding second updated set of path performancemetrics based on the second set of path performance metrics and thesecond metrics, the second updated set of path performance metricsidentifying the aggregate metrics for the corresponding path to theprescribed destination via the network node.
 14. The medium of claim 13,wherein: the aggregate metrics for each of the first and second set ofpath performance metrics are specified as a corresponding plurality oflink metrics for each hop in the corresponding path between theprescribed destination and the network node.
 15. The medium of claim 11,wherein the link metrics include at least one of bandwidth utilization,signal to noise ratio, signal strength, selected link speed, orbandwidth reservation level.
 16. An ad hoc network comprising: aplurality of network nodes, one of the network nodes identifiable as aprescribed destination having one or more source-connecting linksenabling the other network nodes to reach the prescribed destination viapaths, each of the other network nodes having at least one first linkfor reaching the prescribed destination, at least one of the othernetwork nodes having a plurality of second source-connecting linksconnecting the one other network node to respective other ones of theother network nodes, each of the other network nodes comprising: anetwork interface configured for receiving, via the corresponding firstlink, a first set of path performance metrics that identifies aggregatemetrics for a corresponding path to the prescribed destination via thecorresponding first link, the path performance metrics based on at leastinitial link metrics having been output by the destination onto thecorresponding source-connecting link of the prescribed destination, theinitial link metrics describing performance of the correspondingsource-connecting link of the prescribed destination; and a resourceconfigured for: selectively determining second metrics for at least oneof the second source-connecting links providing reachability by thecorresponding other network node to the prescribed destination for atleast one connected network node, and outputting, onto the least one ofthe second source-connecting links having been established by thenetwork interface with the connected network node, an updated set ofpath performance metrics based on the first set of path performancemetrics and the second metrics, the updated set of path performancemetrics identifying the aggregate metrics for the corresponding path tothe prescribed destination via the corresponding secondsource-connecting link and the first destination-oriented link, whereinthe prescribed destination is identified by the corresponding othernetwork node as a directed acyclic graph (DAG) destination and the firstlink is selected by the corresponding other network node as adestination-oriented link that is directed toward the DAG destination.17. The network of claim 16, wherein: the network interface isconfigured for receiving, via a second link of the corresponding othernetwork node, a second set of path performance metrics that identifiesthe aggregate metrics for a corresponding path to the prescribeddestination via the second link; the resource configured for selectingone of the first or second links, based on a comparison between thefirst and second set of path performance metrics.
 18. The network ofclaim 17, wherein the resource is configured for outputting acorresponding second updated set of path performance metrics based onthe second set of path performance metrics and the second metricsidentifying the aggregate metrics for the corresponding path to theprescribed destination via the corresponding other network node.
 19. Thenetwork of claim 18, wherein: the aggregate metrics for each of thefirst and second set of path performance metrics are specified as acorresponding plurality of link metrics for each hop in thecorresponding path between the DAG destination and the correspondingnetwork node.
 20. The network of claim 16, wherein the initial linkmetrics include at least one of bandwidth utilization, signal to noiseratio, signal strength, selected link speed, or bandwidth reservationlevel.